The Federal Communications Commission announced Thursday that it had settled a case involving AT&T after nationwide outages in 2017 left thousands of wireless customers unable to access 911, in some cases for hours. AT&T Mobility will pay a $5.25 million fine and take steps to make sure the problem doesn't occur again, the agency said.

The 911 outages occurred in March and May 2017 when the Dallas-based company was making changes to its network, the FCC said in a news release. During the March outage, which lasted for five hours, about 12,600 calls to 911 were unable to get through, it said. In the May outage, which lasted 47 minutes, there were 2,600 failed calls.

In the March outage, North Texas cities from Dallas to Arlington to Plano reported problems. Local police departments advised callers to use the non-emergency numbers if they needed immediate help.

AT&T customers from about a dozen states from California to Illinois to Florida were also affected.

AT&T issued a statement Thursday after the closure of the investigation by the FCC was announced.

"Providing access to emergency 911 services is critically important, and to that end we cooperated with the FCC in their review. These events resulted from planned network changes that inadvertently interfered with the routing of 911 calls. We've taken steps to prevent this from happening again," the statement said.